What are the physical and chemical properties of natural quartz?

Natural quartz, a mineral composed primarily of silicon dioxide (SiO₂), exhibits a wide range of physical and chemical properties that make it versatile and highly valuable in various industries. Here are its key properties:

Physical Properties

1. Crystal System: Hexagonal.
   • Quartz typically crystallizes in the trigonal division of the hexagonal crystal system.
2. Appearance:
   • Transparent to opaque.
   • Can be colorless, white, pink, purple, yellow, brown, or black depending on impurities (e.g., iron, aluminum, or hydroxyl groups).
3. Hardness:
   • 7 on the Mohs scale, making it relatively resistant to scratching.
4. Luster:
   • Vitreous (glassy) when polished.
5. Density:
   • Approximately 2.65 g/cm³.
6. Cleavage:
   • Lacks true cleavage; breaks with a conchoidal fracture.
7. Optical Properties:
   • Transparent quartz can exhibit birefringence.
   • Has a refractive index of approximately 1.544–1.553.
8. Piezoelectricity:
   • Quartz crystals exhibit piezoelectric properties, generating an electric charge under mechanical stress.
9. Melting Point:
   • High melting point around 1670°C (3038°F) under normal atmospheric pressure.

Chemical Properties

1. Chemical Formula: SiO₂.
   • Composed of silicon and oxygen in a 1:2 ratio.
2. Chemical Stability:
   • Insoluble in water and most acids.
   • Reacts with hydrofluoric acid (HF), forming silicon tetrafluoride (SiF₄).
3. Thermal Stability:
   • High thermal resistance; maintains structural integrity at high temperatures.
4. Reactivity:
   • Relatively inert chemically but can react under extreme conditions, such as high pressure or temperature.
5. Weathering Resistance:
   • Highly resistant to weathering due to its chemical stability and hardness.

Common Variants of Quartz

Quartz comes in several forms depending on its impurities and crystal structure:

• Amethyst: Purple quartz colored by iron and irradiation.
• Citrine: Yellow quartz due to ferric impurities.
• Rose Quartz: Pink quartz, often due to trace amounts of titanium, iron, or manganese.
• Smoky Quartz: Brown or gray quartz caused by natural radiation.

These properties make quartz a critical component in industries like electronics (piezoelectric devices), optics, construction (aggregates), and jewelry.